Data communication in an access network

ABSTRACT

A management device ( 100 ) for use in an access network ( 10, 19, 20, 30, 40, 100 ) including a plurality of data connections ( 18, 19, 20 ) between end user devices ( 10 ) and an aggregation transceiver device ( 20 ) where the connections ( 18, 19, 20 ) are aggregated for onward connection through the access network ( 20, 30,40 ), the access network storing in association with each data connection a Dynamic Line Management, DLM, profile which specifies a set of values for a plurality of parameters associated with the respective data connection, together with a stability level specifying a desired level of stability for the data connection. The device comprises means for receiving monitoring data specifying the stability of each respective data connection over a predetermined period of time; means for selecting a DLM profile to be applied to the connection in dependence on both the monitoring data and the stored stability level associated with the data connection; and means for requesting an OSS system of the access network to apply the selected profile to the data connection.

This application is the U.S. national phase of International ApplicationNo. PCT/GB2008/004211 filed 19 Dec. 2008, which designated the U.S. andclaims priority to EP Application No. 07255002.3 filed 21 Dec. 2007, theentire contents of each of which are hereby incorporated by reference.

FIELD OF THE INVENTION

The present invention relates to data communication. In particular, itrelates to the management of an access network including DigitalSubscriber Line (DSL) connections.

BACKGROUND TO THE INVENTION

Dynamic Line Management (DLM) is a technique for improving the stabilityof DSL connections. It is particularly useful when operating DSLconnections at close to their maximum speed, because under theseconditions external noise affecting the transmitted signal can cause thetransceivers to be unable to successfully recover the signal to betransmitted with sufficient reliability to enable the connection to bemaintained. If this occurs, the connection needs to be re-established.This is referred to as a re-synch and the user notices a temporary lossof service while the connection is re-established. Re-synchs aregenerally found to be particularly annoying by end users.

DLM seeks to minimise such re-synchs by automatically analysing DSLconnections (especially the rate of occurrence of re-synchs) and varyingcertain parameters which can affect the likelihood of re-synchsoccurring (for example the depth of interleaving, the amount ofredundancy built into the encoding used, etc.). Typically, this is doneby using a number of different profiles having various different sets ofvalues for the parameters most likely to have an impact on the stabilityor otherwise of a DSL connection and moving a particular connectionbetween different profiles until a profile is found which has anacceptable stability. The profiles are applied at the local exchange(sometimes referred to—especially in the USA—as the central office)usually within a piece of equipment known as a Digital Subscriber LineAccess Multiplexer (DSLAM) which houses a number of DSL transceiverunits as is well known in the art.

Typically, the profiles are conceptually able to be thought of asranging between more aggressive and less aggressive, where the moreaggressive profiles tend to provide better services to the user (interms of especially higher bit rates and lower latencies) but are morelikely to result in the line being unstable, whereas less aggressiveprofiles tend to offer lower bit rates and/or latencies but greaterstabilities.

An Alcatel Technology White Paper entitled “Dynamic Line Management forDigital Subscriber Lines” discusses DLM and suggests in overview animplementation in which there is a Validation Phase and an Operationsphase. In the validation phase a connection is monitored fairlyintensively to identify an appropriate profile for the line andthereafter it is monitored less intensively to ensure that theoriginally selected profile continues to remain valid. This paper alsomentions that operators define “a set of policies for each serviceclass”; this implies that different service classes may have differentpossible profiles between which they may transition. Thus, for example,for a service class associated with streaming video to an end user, theoperator may enforce interleaving since there is rarely a need for avery low delay, but reliability is important to maintain a good qualitypicture. Furthermore, very high bandwidth is also often not required andso the operator may take away very low margin profiles as an option forsuch a service class (even where a line might be able to support them).

Co-pending European patent application No. 07250428.5 describes anearlier DLM solution devised by the present applicants in which veryunstable data connections are detected in an efficient manner andcorrective action is taken within a relatively short period of timewhilst data connections which are not very unstable are monitored andtransitioned between different profiles based on more thoroughmonitoring over a longer time-scale.

US published patent application No. 2006/0198430 describes a DLMsolution in which various rules such as transition matrices are used todetermine under what circumstances a transition should be made from oneprofile to another.

All of the DLM solutions known to the present applicants are able to setvarious parameters in order to try to maintain the lines at what isdeemed to be an acceptable level of stability. However, the presentinventors have now realised that this results in an inflexible solutionwhich is less than optimally suited to an access network in whichdifferent DSL connections may be used for different purposes.

SUMMARY OF THE INVENTION

According to a first aspect of the invention, there is provided a methodof operating an access network including a plurality of data connectionsbetween end user devices and an aggregation transceiver device where theconnections are aggregated for onward connection through the accessnetwork, the method comprising: storing a plurality of differentprofiles, each of which specifies a set of values for a plurality ofparameters associated with each data connection, and further storing, inrespect of each of the connections, a stability level and performing thefollowing steps: for each data connection, monitoring the performance ofthe connection; selecting one of said stored profiles to be applied tothe connection in dependence on both the results of monitoring theconnection and the stability level associated with the data connection;and applying the selected profile to the data connection.

Thus the method of the present invention permits different stabilitypolicies (each of which corresponds to or specifies a stability level)to be applied to different data connections to reflect the differentpossible uses for the connection which may place different values on therelative merits of line stability, bandwidth and latency. The differentstability policies preferably control the circumstances under which aconnection will be transitioned between different profiles (for exampleby tolerating a greater number of errors or resynchronisations per unittime before transitioning to a less aggressive profile and vice versa).

The allocation of a stability policy to a particular line may be basedon a number of different factors. Preferably the end users' wishes inthis respect will be an important factor, and preferably differentstability policies may be applied to lines operating with the same basicservice class. Thus for example, two users having a basic broadbandconnection (i.e. one intended for general Internet use rather than aline dedicated to providing streaming video etc.) might use thoseconnections for different purposes. For example, one user may simplyperform fairly low bandwidth hungry internet browsing and videostreaming, another may use it to perform large downloads of data, andanother might use it for on-line gaming purposes. These different usersmay well have very different tolerances to stability levels. Forexample, the first user, who does not generally place any great demandson the broadband connection, may well be less tolerant to errors anddrop-outs and thus would prefer generally to achieve a greater stabilityat the risk of perhaps having a slightly lower maximum bandwidthavailable, compared to the second user who would on the whole prefer tohave a slightly less stable connection but one which (when it isconnected) can achieve high throughputs.

Preferably, the results of the monitoring of the stability of each lineinclude a parameter representing the number of forced resynchronisationsoccurring within a predetermined period of time (e.g. within a 24 hourperiod), and the stability level determines a pair of thresholds foreach such parameter which if exceeded will cause a transition to be madefor that particular connection from one DLM profile to another. Forexample an aggressive (relatively unstable) stability level mightrequire more than 10 forced resynchronisations within any given 24 hourperiod to occur in order for the system to decide to transition theconnection from its current DLM profile to a more stable DLM profile,whereas a transition for a connection associated with a normal stabilitylevel, might be triggered by detecting more than 5 forcedresynchronisations within any one 24 hour period; and one associatedwith a very stable desired stability level might be transitioned to anew more stable DLM profile if more than 1 forced resynchronisation isdetected in any given 24 hour period. A more detailed discussion of thismechanism is given below. If such a threshold has not been exceeded,then the connection stays on its current profile. On the other hand if athreshold in the other direction is exceeded (note this could operate ona different normally longer, timescale) then the connection might betransitioned to a less stable profile in order to improve bandwidth orlatency etc. Thus for example, if a connection associated with anaggressive (i.e. relatively low desired level of stability) determinesthat no more than one forced error has occurred per 24 hours for say 6consecutive 24 hour periods, then it may be transitioned to a moreaggressive profile, whereas a connection desiring very stableperformance might only transition to a more aggressive profile if it isdetected that there have been no forced resynchronisations within a 30day period, etc.

Preferably two main parameters which control the operation of xDSLconnections are varied to generate different profiles, theSignal-to-Noise Ratio (SNR) margin and the fast/interleave mode. Notethat the stability policies in general do not affect the profiles whichare available for a particular line to transition between, but ratherthe circumstances under which such a transition will occur. In the priorart solutions, of which the applicant is aware, the same thresholds(e.g. in terms of the number of errors and/or dropouts per unit time)are used for determining that a particular profile is feasible or nothave been used, regardless of the service class, etc. This has lead toan inflexible system in which it is impossible to allow some customersto specify that they want very stable lines, whilst others have lineswhich are less stable (but have the prospect accordingly of achievinggreater bandwidth rates). By contrast, in preferred embodiments of thepresent invention different thresholds are used to determine when totransition from one profile to another depending on the associatedstability level of the line in question.

The SNR margin represents the amount of redundancy built into theselected bit rate (and other connection options) for the connection,given the measured value of the actual SNR experienced by the modem.Thus, each possible set of significant values for the connectionparameters (i.e. bit-rate, level of trellis coding, level of interleave,etc.) has a corresponding baseline SNR which represents the minimumvalue of the SNR at which the connection would be expected to operatewith a Bit Error Rate (BER) of 10⁻⁷ (i.e. 1 bit is expected to be inerror for every 10⁷ bits); this BER of 10⁻⁷ is called the target rate asthe connection is expected to operate very well with this level of BER.The SNR margin represents the amount (in decibels) by which the actualmeasured SNR exceeds this baseline amount at the time of setting up theconnection. Thus the actual received SNR may vary over time, aftersetting up the connection, below the measured amount at setting up theconnection by up to the amount of the margin and still the connectionwould be expected to operate with a BER of less than or equal to thetarget amount (i.e. at least as good as the target amount).

The definition of SNR margin which is given in the xDSL standard ITUG992.1 Section 9.5.1 is: “Signal-to-Noise Ratio (SNR) margin: Thesignal-to-noise ratio margin represents the amount of increased receivednoise (in dB) relative to the noise power that the system is designed totolerate and still meet the target BER of 10-7, accounting for allcoding (e.g. trellis coding, RS FEC) gains included in the design. TheSNR margin ranges from −64.0 dB to +63.5 dB with 0.5 dB steps.”

It will thus be appreciated, that the lower the SNR Margin, the higherthe headline bit rate that will be achievable (i.e. assuming that thereare no errors). Whilst, the higher the SNR Margin, the more likely thatthe connection will operate in a stable manner, even in a fluctuatingnoise environment.

Fast/interleave mode switches the depth of interleave between nointerleave (FAST mode) and any of the depths of interleave defined inthe currently applicable ADSL standards (e.g. the ITU G.992.xstandards). In many implementations, only the lowest level of interleave(a depth of 2, where units in a single code word which are adjacentbefore interleaving are separated by one interleaved unit from anotherword after interleaving) is used at the moment; however, this may changein the future. As is well known in the art, use of interleave protectsagainst short duration noise spikes by interleaving units (e.g. bytes)of a certain number (depending on the depth of interleave) of code words(each comprising several units) where each code word has a certainamount of error protection such that a relatively small number oferrored units per code word can be recovered by the error protectionmechanism to recover the original code word completely (e.g. if thereare 5 units (e.g. bytes) per code word and the error correctionmechanism can recover code words where one unit is errored, aninterleave depth of 2 would enable both interleaved words to both berecovered if a noise caused two adjacent units within a two wordtransmission period to become corrupted). Interleaving providesprotection against impulsive noises at the expense of increased latency(and greater buffering requirements of network equipment).

The functionality (or sub-components of this functionality) of thepresent invention may be performed by a number of different devices. Inparticular, the stability level may be stored within the aggregationtransceiver device (e.g. the DSLAM) or a device associated therewith.This would correspond to an embodiment in which the access networkcontroller/operator takes responsibility for implementing differentstability policies for different data connections. This is particularlyadvantageous where this is the party which has control for switchingbetween different connection profiles (as is generally the case) and forcases where the connection does not wish to transition between differentstability policies on a very frequent basis (e.g. depending on theparticular application being used by the user device at any particulartime) since this could cause difficulties for a centralised system whichhas to deal quickly with what could potentially be very many customers.

In an alternative embodiment, however, the stability policies may bestored at the respective end user device. Based on the selectedstability policy (and with suitable knowledge of the level of stabilitywhich the DSLAM is attempting to provide for that data connection) theuser device may include some functionality (e.g. provided by a suitablecomputer program) which intercepts messages from the DSL modem of theend user device destined for the network side DSL modem (e.g. located inthe aggregation transceiver device) and modifies these messages so as tocause the network side DSL modem to set up a DSL connection which ismore or less aggressive (in terms of bandwidth or latency or both) thanif the messages had not been so modified. Equivalently, the normaloperation of the DSL modem could simply be altered such that fordifferent stability levels or policies the modem generates differentmessages to be returned to the network side DSL modem.

An example of a computer program which operates in this general mannerand which could (preferably with some suitable modifications discussedbelow) be used for this purpose is the “DMT tool” which is available fordownload at http://dmt.mhilfe.de/. This program operates by sendinginformation about characteristics of the connection (especially the SNR)which is not based purely on what has been detected by the modemaccording to the normal operation of the modem. Instead, with the DMTtool, this information may be input directly by a user of the tool, thusover-writing the information that would normally be sent by the modem.However, in a preferred embodiment of the present invention, thisprogram would not be used to modify the SNR values (or would not be usedonly to modify the SNR values) reported by the end user modem to thenetwork-side modem, but rather (or in addition) the number of errors(especially the number of errored seconds) occurring in the downstreamdirection which are dependent upon the actual measured characteristicsas well as the stability level associated with the currently in forcestability policy for the connection.

Preferably, in all cases, the different profiles are all stored at thenetwork side (e.g. at the DSLAM) and the network operator hasresponsibility for selecting the actual profile applied to a connection,though this is usually done at least partially in response to messagescoming from the end user's DSL modem. Preferably, the parameters used todetermine whether or not a change of profile should be made include thenumber of times that a re-synch has occurred on a DSL connection withina certain period of time and the number of errored seconds which haveoccurred within a certain period of time (e.g. within the past 24hours).

Preferably, the system additionally includes a stability policy selectorwhich selects an appropriate stability policy based on the usage (orintended or requested usage) of the connection. Preferably the selectoris user or operator configurable and it preferably acts as a statemachine, whereby some circumstances may result in a new policy beingadopted for some states of the selector but not for others. For example,the selector may have three states of aggressive, normal and stable andmay be configured such that if the selector is in the stable state andthe user switches from a video streaming application to web-browsing,the selector may change state from stable to normal, while if theselector is in the aggressive state and the user switches from a gamingapplication to web-browsing, the selector may not change state, etc. Aswith the storage of the stability level or policy, this selector couldalso be implemented either at the end user side of the DSL connection(corresponding to the embodiment where control of the stability policylies with the end user device) or at the network/DSLAM side of the DSLconnection (corresponding to the embodiment where the network operatorhas responsibility for the currently applied stability level or policyfor the connection).

Preferably, the selector includes means for causing a re-synchronizationof the DSL connection where it transitions from one state to another.

Preferably, the data connections are digital subscriber lines includingremote and central transceiver-units connected over a copper pair andoperating in accordance with one or more of the various xDSL standardsagreed by the International Telecommunication Union (ITU) (e.g. G.992.xand their annexes). Preferably the aggregation transceiver device is aDigital Subscriber Access Multiplexer (DSLAM).

Preferably the profiles are ranked according to a level ofaggressiveness, where more aggressive profiles are, in general, morelikely to result in a connection becoming unstable.

According to a second aspect of the invention, there is provided amethod of operating an access network including a plurality of dataconnections between end user devices and an aggregation transceiverdevice where the connections are aggregated for onward connectionthrough the access network, the method comprising: storing a pluralityof different profiles, each of which specifies a set of values for aplurality of parameters associated with each data connection, and, foreach data connection, monitoring the performance of the connection;selecting one of said stored profiles to be applied to the connection independence on the results of monitoring the connection; and applying theselected profile to the data connection, wherein monitoring theconnection includes determining or estimating number of times that theconnection resynchronises, within a given period of time, as a result ofan automatic or forced resynchronisation and using the determined orestimated number of forced resynchronisations when selecting a profileto apply to the data connection.

In accordance with the above set out second aspect, the metric of thenumber of resynchs per unit time is modified to remove (generallyspeaking, at least some of) the resynchs caused by user action ratherthan as a result of the line experiencing technical problems orinstability, etc, thus providing a more useful metric for use inperforming Dynamic Line Management.

An automatic or forced re-synchronisation is one which occurs becauseerrors on the connection cause a complete loss of connection. When thisoccurs, the end modems revert to an initial state in which a connectionis re-established from scratch, rather than trying to rescue theprevious connection. This is set out in the various xDSL standardsincluding, in particular, ITU-T G992.1—ADSL1, ITU-T G992.3—ADSL2, ITU-TG992.5—ADSL2+ and ITU-T G994.1—Handshake Procedures for digitalsubscriber line (DSL) transceivers.

Preferably, determining or estimating the number of forcedresynchronisations comprises determining the total number ofresynchronisations (in the given period of time of interest) for allreasons, estimating the total number of those resynchronisations causedby a user and subtracting this estimated number of user causedresynchronisations to obtain an estimate for the number of forcedresynchronisations.

Preferably, the step of estimating the number of user causedresynchronisations comprises detecting that more than a predeterminedminimum period of time prior to or after a resynchronisation has elapsedwithout a connection having been established and without the lineautomatically attempting, but failing, to re-establish the connection.Thus if the user simply switches off or unplugs the modem for a periodof time greater than the minimum period of time, the resultingre-synchronisation is determined to be a user caused re-synchronisationrather than a forced resynchronisation. Preferably this is achieved bycounting the contiguous periods of downtime exceeding the predeterminedminimum period within the (longer) given period.

In one embodiment, a record is kept of each 15 minute period (bin)during which there is no connection in place, and the number of sets ofcontiguous periods in which no connection is recorded as being in placewithin any 24 hour period (batch) is taken as the estimated number ofuser caused resynchronisations within that 24 hour period; naturally, inalternative embodiments, different periods of time may be used for thebins or for the batches (e.g. 5 minute period bins and 48 hour batches,etc.). The number of contiguous periods (bins) may conveniently bedetermined by counting the number of transitions between periods (bins)in which no connections is recorded as being present and periods (bins)in which a connection is recorded as being present.

Further aspects of the present invention relate to systems, devices,computer programs and carrier means or media as set out in theaccompanying claims, especially tangible carrier means such as opticalstorage devices (e.g. compact discs (CD's) or DVD's), or magneticstorage devices such as magnetic discs, or non-volatile solid-statememory devices.

BRIEF DESCRIPTION OF THE FIGURES

In order that the present invention may be better understood,embodiments thereof will now be described, by way of example only, withreference to the accompanying drawings in which:

FIG. 1 is a schematic block diagram illustrating a telecommunicationsnetwork incorporating a management device operating in accordance with amethod according to the present invention;

FIG. 2 is a schematic block diagram illustrating the management deviceof FIG. 1 in more detail; and

FIG. 3 is a flow diagram illustrating the steps carried out by themanagement device of FIG. 1 in order to control the DLM profile appliedto the DSL connections in the network of FIG. 1.

DETAILED DESCRIPTION OF EMBODIMENTS

The main embodiment described below uses a management device 100 toperform two principal functions—Broadband Remote Access Server (BRAS)provisioning and Dynamic Line Management (DLM). The BRAS provisioning isdescribed in brief in this application, for the sake of completeness,but it is described in greater detail in co-pending International patentapplications GB2006/002826 and GB2006/002818 both filed on 28 Jul. 2006,referred to above, for readers interested in the particulars of thepreferred methods of BRAS provisioning applicable to the mainembodiment.

As for the DLM function, this is desirable in the main embodimentbecause the downstream speed of the ADSL connections controlled by themanagement device of the main embodiment rate adapts to the highestspeed the line can support from 2 Mb to 8 Mb. As the ADSL connectionsare running at their maximum limits they are more susceptible to noisewhich can cause errors and spontaneous resynchronisations (resyncs).

In overview, the role of the DLM function of the management device is toensure that the ADSL connections provide a good compromise between thestability of the line and the performance of the line in terms of bitrate (or perhaps more importantly the rate at which a user can receivedesired data—after any lost packets caused by errors have been re-sent,for example) and latency. The DLM function does this by receiving datafrom DSLAM Data Collectors each day and processing this received data.The DLM function is then able to increase or decrease the noise margins(i.e. the SNR margins) and/or interleave levels as required by setting anew profile for each ADSL connection (using the existing provisioningsystems for setting profiles at DSLAM's). This basic functionality isenhanced with logic to minimise churn or oscillation of profiles (byattempting to stabilise the DSLAM profile for each connection, ratherthan reacting to every relevant change in the environment of theconnection which could cause the maximum stable profile applicable tochange).

Main Embodiment

Referring to FIG. 1, a first embodiment of the present invention isillustrated in overview. A copper pair loop 19 (which forms part of theaccess network which extends between customer premises equipment 10 andthe BRAS 40) connects customer premises equipment 10 to a DSLAM 20located within a local exchange (also known as a central office in theUS). The DSLAM separates normal voice traffic and data traffic and sendsthe voice traffic to the Public Switched Telephone Network (PSTN) 70.The data traffic is passed on through an Asynchronous Transfer Mode(ATM) network 30 which forms the remainder of the access network 19, 20,30 (in the present embodiment, the ATM network 30 is British Telecom(BT)'s Multi Service intranet Platform (MSiP) ATM network). Connected tothe ATM network 30 is a Broadband Remote Access Server (BRAS) 40 atwhich several IP traffic flows or ATM circuits from (and to) multipleService Providers (SP's) 62, 64, 66 are aggregated (and disaggregated)via an IP network 50 (which in this case is BT's Colossus IPnetwork)—which itself may run over an ATM network or networks. Withinthe customer premises equipment 10, there is an ADSL splitter filter 18,a telephone 12, an ADSL modem 16 and a computer 14.

In some cases the first hop of an IP packet travelling from computer 14towards an ISP 62, 64, 66 would be the BRAS 40; whereas in other casesthe first hop from an IP perspective could be beyond the BRAS 40.

In all cases, the end user's modem 16 creates a Point-to-Point Protocol(PPP) session from the modem to another device in the network. This is alogical end to end connection that carries the end users traffic fromthe modem to the target IP network.

In some cases (e.g. in BT's Central+ product), the PPP session isterminated on the BRAS, and then onward routed directly onto theInternet (e.g. via a core IP network such as BT's Colossus network).

In one example configuration where the PPP session is not terminated atthe BRAS 40, the PPP session is terminated on a “home gateway” at theedge of the core network, connected to the Service Provider (SP). Inanother example configuration (e.g. such as in the BT central product) aLayer 2 Tunnelling Protocol (L2TP) tunnel is used to pass through theBRAS 40 to a terminating BRAS which belongs to the SP; the L2TP tunneltunnels all the PPP sessions into the SP network for them to handle asthey want.

In all cases, the first IP hop is from the end user to the terminatingBRAS (i.e. over the PPP connection). Furthermore, in all cases, the BRAS40 is responsible for policing the amount of traffic flowing downstream(i.e. from the network towards the customer premises equipment) towardseach line connected to the BRAS 40, to ensure that it does not exceed amaximum amount provisioned for that line. This policing is either doneat the IP layer (where the BRAS 40 terminates a PPP connection from thecustomer premises equipment 10) or at a lower level (e.g. at the ATMlayer) where there is some sort of sub-IP layer tunnelling through theBRAS 40.

The above mentioned arrangement of items 10, 19, 20, 30, 40, 50, 62, 64,66 and 70 is conventional. However, in addition to this conventionalarrangement, in the present embodiment there is a management device 100which communicates with both the DSLAM 20 and the BRAS 40. The detailedoperation of this device (especially as regards its DLM function) isexplained in greater detail below with reference to FIGS. 2 and 3.However, in overview it obtains information from the DSLAM 20 about therate at which each Digital Subscriber Line (DSL) connects to the DSLAMand information about events such as detected errors and/or resyncsoccurring on the line/connection and modifies the operation of theDSLAM's as regards the aggressiveness of the profile used by arespective DSLAM for a respective DSL connection.

As shown in FIG. 2, the management device 100 comprises two mainfunctional parts, a BRAS provisioning or BRAS control function 120 and aDynamic Line Management (DLM) function 110.

The BRAS provisioning function 120 processes part of the informationreceived from the DSLAM's to assess a consistent connection speedachieved by each DSL. If it determines that this consistent rate hasincreased as a result of recent higher rate connections, it instructsthe BRAS to allow higher through flows of traffic for that DSL. On theother hand, if it detects that a particular connection speed is belowthe stored consistent value, it reduces the consistent value to thecurrent connection rate and immediately informs the BRAS of the newconsistent value rate so that the BRAS does not allow more traffic toflow to the DSL than the DSL is currently able to cope with.

Precise details of some of the algorithms which may be used by the BRASControl function 120 of the management device 100 to calculate aconsistent rate in the present embodiment are described in copendingInternational applications GB2006/002826 and GB2006/002818. However, itshould be noted that the intention of these algorithms are to arrangethat the user will receive data at the highest rate which his/her DSL isconsistently able to obtain without requiring the BRAS to bereconfigured every time the DSL is connected at a new maximum rate. Atthe same time the algorithms seek to ensure that if a DSL connects at arate which is below that at which the BRAS is currently configured toallow data through for that DSL, then the BRAS is quickly reconfiguredto avoid overloading the DSLAM.

Details of the particular algorithm employed in the present embodimentby the DLM function are set out below. In overview however, a DLM datareceiving sub-function receives a new file daily from each elementmanager containing up to 96 timeslots (15 minute period) per DSLconnection per day together with information about a stability policy orlevel associated with each connection. This data is used in a DLManalysis sub-function to determine if changes to the DSLAM profile arerequired to stabilise the end users service to comply with theconnection's respective associated stability policy or level. If changesare required, a DLM output sub-function sends a request to theOperational Support System (OSS) of the access network for the profileapplied to the line to be changed. The precise way in which this isperformed will depend on the details of the OSS of the particular accessnetwork and is not relevant to the present invention and so will not bedescribed further herein.

Each of the DLM sub-functions mentioned above is implemented by standardcomputer processor components operating in accordance with software codemodules stored in a memory 112 forming part of the DLM function 110; inparticular, a DLM data receiving code module 114 (DATA IN) causesimplementation of the DLM data receiving sub-function, a DLM analysiscode module 116 (DATA ANALYSIS) causes implementation of the DLManalysis sub-function and a DLM output code module 118 (DATA OUT) causesimplementation of the DLM output sub-function. Additionally, the memory112 also stores the stability policy data set 115 (STABILITY POLICIES)in which the stability level or policy associated with each DSLconnection managed by the management device is held. Furthermore, in thepresent embodiment, the memory 112 also stores a forced resyncronisationestimation module 117 (FORCED RESYNCHS EST.) for implementing asub-function to estimate the number of resyncronisations for each linein each batch of data caused as a result of some sort of error, etc.occurring in the connection rather than as a result of user actions(e.g. to switch off or disconnect their DSL modem). This forcedresynchronisation estimation sub-function is described in greater detailbelow.

It should be noted that in the present embodiment, the data receivingsubfunction (114) constitutes the claimed receiver for receivingmonitoring data specifying the stability of each data connection over apredetermined period of time, the DLM analysis code module constitutesthe computer program code module for causing the processor to determinewhether each data connection should be transitioned onto a new profilein dependence upon both the monitoring data and the stability levelassociated with the data connection and the computer program code modulefor causing the processor to select a new DLM profile to be applied toeach connection in the event that the processor determines that thecorresponding data connection should be transitioned onto a new DLMprofile; and the DLM output sub-function (118) constitutes the claimedrequestor (see claim 10).

The main source of input data for the DLM function is a daily file fromeach element manager, giving an aggregated report of each line'sactivity over the preceding 24 hours. This results in a change in DSLAMprofile being applied no more frequently than once every 24 hours whichis advantageous because it avoids the possibility of the DSLAM beingreconfigured every time a line re-syncs. In addition however, the DLMfunction additionally receives input data specifying a stability levelfor each line. In the present embodiment, this is input from a databaseinto which the data is manually entered by an operator as part of theprocess of provisioning a new DSL connection and is stored within thestability policies data set 115 within the DLM memory 112. Thus in thepresent embodiment, the intention is that when a customer orders a DSLconnection he/she is offered different levels of stability (which willbe most suitable for certain different types of activity); thuscustomers who mostly intend to use the connection for video streamingwill benefit from a stable connection, whereas customers mostly usingtheir connection for downloading large files, etc. would benefit from ahigher bit-rate rather than from very high stability levels.Alternatively, instead of providing this facility on an end-user byend-user basis, retail customers (i.e. Service Providers) of the networkservice operator (i.e. a wholesale network operator) could be providedwith the option to select a stability level on behalf of their customersand could sell this on to their (end user) customers as a “specialised”product offering.

However, in alternative embodiments, the stability level could beupdated more dynamically, as a result of a request by the user. In anexample embodiment, a web server could be provided to receive userrequests for a change of stability level (perhaps with a maximumpermitted frequency of requests permitted per user, e.g. no more thanone per hour or one per day, etc.) and this could then cause the DLMfunction as soon as possible to re-run it's comparison process for thatline with the newly requested stability level and, if as a result of thecomparison it is determined appropriate to transition to a new profile,then to transition to the new profile, again as soon as possible so thatthe user experiences a fairly dynamic response to a request to changethe stability level.

Each time a line is checked to see if its profile should be changed(which in the present embodiment occurs once every 24 hours as part of abatch processing function), the corresponding stability level associatedwith that line is read and then threshold values for, that line are setdepending on the stability level associated with the respective line.The daily file data is then processed and the data for the respectiveline being analysed is compared with the threshold values set for thatline in dependence upon the stability level associated with the line. Ifthe comparison indicates that a transition should be made, then acorresponding instruction is issued to the OSS system for acorresponding transition to be made.

The DSLAM profile has two parameters which are adjusted in the variousdifferent profiles available for the DLM function to choose between inorder to improve the stability of the line or conversely to improve thebit-rate or low-latency of the connection: the target margin and the runmode (the latter enabling the use of interleaving). The default lineprofile which is initially applied to all lines has a target margin of 6db and interleaving disabled (often referred to as being in fast mode).Changing these parameters is based on two performance metrics in thepresent embodiment, errors (in particular, in this embodiment, errorscaused by code-violations) and re-trains (i.e. re-syncs).

The number of errors and re-trains is normalised to up-time (totalsynchronised time during the period) to form the actual performancemetrics used to determine the stability of the line. For example 100errors in 10 hours of up-time after normalisation is (quite sensibly)very different from 100 errors in 1 minute of up-time. The normalisationis performed by calculating a mean-time-between either errors orre-synchs. Furthermore, in the present embodiment, the re-trainsparameter is also processed, prior to use as a stability performancemetric, by discounting the number of resynchs deemed to be user-causedresynchs, prior to calculating the mean-time-between resynchs. In thepresent embodiment, this is achieved using the following method, asspecified below according to the following pseudo-code:

[Note the following assumes that an array uptimes[ ] has been formed andpopulated, such that each element in the array corresponds to one of the96 15-minute bins per 24-hour period (in the present embodiment) for aparticular DSL connection—the type of the array (i.e. 1 bit numbers, 1byte integers, short integers, floating numbers, etc.) is unimportant solong as where an element of the array is zero it indicates zero uptimein the corresponding bin and a non-zero value indicates that there wasat least some uptime in that bin—if 1-bit values are used they may beconsidered as taking either a True or a False value, in which case oneof these should be used to indicate zero uptime instead of zero—however,in the present embodiment, each element comprises a short integerbetween 0 and 900 specifying the number of seconds of uptime in therespective 15-minute (i.e. 900-second) bin.]

*** Comment—method to count number of unforced re-trains in a 24-hourperiod for a given connection

SET unforcedretrains = 0 FOR (i = 0 to 95) (   IF (uptimes[i] = 0 ANDuptimes[i+1] != 0) THEN   unforcedretrains++   ) RETURNunforcedretrains.

The above pseudo-code basically says to check each bin and determine ifit has zero uptime whilst the subsequent bin has non-zero uptime (i.e.detecting a transition from a bin with no uptime to a bin with someuptime) and for each such transition to increment the variableunforcedretrains which thus keeps a running total of the number of(assumed-to-be) user-caused re-synchs. This value is then subtractedfrom the total number of retrains detected for the respective connectionwithin the 24 hour period to obtain an estimated number of forcedretrains for the 24-hour period and then the total uptime in seconds isdivided by the estimated number of forced retrains to obtain anestimated mean time between re-trains in seconds. In the presentembodiment, the uptimes[ ] array stores the number of seconds of uptimein each bin so that it is easy to obtain the total uptime for theconnection by simply summing the values of all of the elements in thearray.

Having calculated the metrics to be used in assessing the stability ofthe line, a check is made against thresholds, etc. as described ingreater detail below, and if it is deemed necessary or desirable achange in profile will be made.

In general, if a move to a less aggressive profile is deemed necessary,a move over to an interleaved profile is made in preference to anincrease in the target margin. Initially an interleaved profile is setwith the same corresponding target margin as the previous fast modeprofile (i.e. 6 dB fast would transition to 6 dB interleaved).

If a customer has opted-out of the option to apply interleaving (e.g.because low latency is more important to them than maximum bit-rate—suchas is often the case for customers who are on-line gamers or VOIP orvideo conference users) then transitions are only made between fast modeprofiles (only the target margin is varied). This clearly limits thecapability of the DLM process.

Before a transition is made, a check is made against line rate to ensurethat a line is capable of making the transition to a new profile withoutsuffering a bit rate drop so drastic that it would fall below apredetermined minimum acceptable bit rate. A transition is only made ifthere is some confidence that the line will be capable of supportingservice above this minimum acceptable rate once the new profile isapplied. For example, in the present embodiment a transition to a highernoise margin profile is only made if the current bit rate isapproximately 800 kbps greater than a Fault Threshold Rate (FTR) (theFTR represents the minimum acceptable bit rate as determined by thenetwork operator—in the present embodiment, the network operator is awholesaler of network services and supplies these services to networkretailers, or Service Providers, who in turn supply consumers; theMaximum Stable Rate is a parameter which is determined by the wholesalernetwork operator and provided to the service provider as an indicationof the estimated capability of the line, the FTR is related to the MSRbut is set below this and is used to trigger a fault report if theconnection rate ever falls below the FTR since this is an indicationthat the line is performing significantly below the rate that it isbelieved to be capable of operating at). If the line is unstable and yetcannot make the transition because it would drop below its minimumacceptable bit rate (i.e. the FTR), then this is flagged for furtherinvestigation. In the present embodiment, the FTR is initially set at 2Mbs and is then re-set to 80% of the Maximum Stable Rate detected by thenetwork during the first 10 days of operation of the DSL in its rateadaptive mode.

If a line fails to synchronise then a transition will be made to a lowertarget margin. If this means returning to a previously unstable statethen this is flagged for further investigation as the line is noteffectively stabilised (even though it isn't at the maximum targetmargin). The line is returned to the previous unstable state so thatsome level of service can be provided to the customer whilst aninvestigation takes place.

If a line fails to synchronise even at the lowest target margin then itis flagged for investigation. For example, it may not be able to supportthe required service or the line may be faulty.

Similarly, if a line is still unstable at the maximum possible targetmargin then it is flagged for further investigation. For example theline may be faulty.

If a line is completely stable then in general the DLM function movesthe line to a lower target margin (or interleave depth) to increase theavailable capacity (or reduce the latency) on the line (remember 3dB≈800 kbps). However, these transitions are handled carefully to avoidfrequent changes in target margin (or interleave depth) up and down.Thus if a line has previously been moved from a more aggressive lowertarget margin (or less interleaved) profile to the current target margin(and interleave depth), it must wait a considerably longer time (e.g. aweek, or a month) before being re-transitioned back to the lower targetmargin (or interleave depth) profile than if it has not previously beenmoved back from the lower target margin (or interleave depth) profile.

In the present embodiment, there is a manual process to enable thetransition between any line profile (e.g. 3 dB fast straight to 15 dBinterleaved is possible by manual intervention).

In the present embodiment, those lines, which have been flagged forfurther investigation are pro-actively repaired in the hope that theycan be repaired before any fault report is generated.

Re-profiling requests to move to a less aggressive profile can occur ona daily basis. Re-profiling decisions on stable lines to move to a moreaggressive profile to increase overall capacity are made over a longertime period (which generally increases with the number of times that theline has previously been moved off the target profile because of lack ofstability issues) as discussed in the preceding paragraph.

In the present embodiment, each line is categorised by the firstsub-function of the DLM function into one of four different categoriesin dependence upon the normalised number of errors and/or re-syncs asreported to the DLM function in the bulk file. The categories correspondto very poor, poor, acceptable and very stable.

The basic flow of the DLM process is shown in Table 1 below.

TABLE 1

In the present embodiment, the general progression through the profilesshown in Table 1 is as follows: if a line is to be changed to a morestable profile, the first change is to move to the profile with the sametarget margin but in interleaved mode instead of fast mode, if the lineis already in an interleaved mode, then the line is moved to the nexthigher target margin profile also in interleaved mode. If the line is tobe moved in the direction of increased capacity, it is kept in the samemode (i.e. fast or interleaved) but moved to the next lower targetprofile, unless it is at the minimum target margin in interleaved mode,in which case it is moved to the minimum target margin profile in fastmode.

In the second sub-function of the DLM function, a line categorised asvery poor is immediately moved two steps in the better stabilitydirection (e.g. from 6 dB Fast profile it would move to 9 dBInterleaved, from 6 dB Interleaved it would move to 12 dB Interleaved,etc.). A line categorised as poor is immediately (although with lowerpriority than the re-profiling of any very poor categorised lines) movedone step in the better stability direction (e.g. from 6 dB Fast to 6 dBInterleaved or from 9 dB interleaved to 12 dB Interleaved). A linecategorised as acceptable is maintained on its current profile (i.e. noaction is taken). A line categorised as very stable is moved (if thefurther requirements to avoid oscillations etc. are also satisfied) onestep in the higher capacity direction (e.g. from 6 dB Fast to 3 dB Fast,from 9 dB Interleaved to 6 dB Interleaved or from 3 dB Interleaved to 3dB Fast).

In the present embodiment, each line is processed once every 24 hours todetermine how the line should be categorised, and thus if a new profileshould be selected for that line. In order to avoid frequentoscillations between adjacent profiles, a good and a bad delay counterare used to place a delay on how quickly a line is reprofiled. Thus,every time a line is categorised as good a good delay counter isincremented (and a poor delay counter is decremented) and only once thegood delay counter has reached a good threshold (which in the presentembodiment is set to 13) is a request made to the OSS for the profile tobe increased by one step to a more aggressive level, and then the delaycounters are reset. Furthermore, every time a line is categorised aspoor, a poor delay counter is incremented (and the good delay counter isdecremented) and only once the poor delay counter reaches a poorthreshold (which in the present embodiment is set to 3) is its profiledropped by one step to a less aggressive level. The delay counters arenever decremented below 0 such that even if a line has experienced anumber of good days (such that the poor delay counter has beendecremented to zero, e.g. five good days in a row) only 3 days in a rowof the line behaving poorly are required for the poor threshold to bereached causing a re-profiling. Furthermore, a delay doubler is used toincrease the delay (i.e. by increasing the good threshold) requiredbefore a line which has moved down from a more aggressive profile to aless aggressive profile level is allowed to re-transition back up to themore aggressive level. The delay doubler is therefore incremented (inthe present embodiment up to a maximum of 5) whenever the line isre-profiled to a less aggressive level and then the delays are reset (asin the case where the line is re-profiled to a more aggressive level).Resetting the delays is done according to the following formulas:GOOD THRESHOLD=DEFAULT GOOD THRESHOLD*2EXP(DELAY DOUBLER)POOR DELAY COUNTER=GOOD DELAY COUNTER=0

The DEFAULT GOOD THRESHOLD is set in the present embodiment to 13 (i.e.equivalent to 14 days), the DEFAULT POOR DELAY is set in the presentembodiment to 3 (i.e. equivalent to 3 days) and the DELAY DOUBLER is setto 0, thus the initial good delay is 13 but each time the line's profileis transitioned to a less aggressive profile the DELAY DOUBLER isincremented until after 5 such transitions, each time the DELAY is resetit is reset to a value of 448 (i.e. equivalent to approx 14 months). Inthe present embodiment, if a user's stability policy or level is changedthe delay doubler is reset back to zero; furthermore, the delay doublerand even the delay counter may be manually reset by an operator to caterfor exceptional circumstances.

In the present embodiment, the specific functionality of the DLMfunction to permit different lines to operate at different levels ofstability according to stability policies set for each line, is nowdescribed below with reference to FIG. 3. In brief, in the presentembodiment, before the DLM performs its line categorisation function fora particular line, it's associated stability level is determined andthen the categorisation is based on the threshold values associated withthe respective stability level, each stability level having a differentset of associated threshold values for use in the categorisationfunction. Thus, at step S5 the stability level for the particular lineto be categorised is obtained together with the delay data stored forthat line (i.e. the current value for the delay counter, DELAY, which,as mentioned above, is initially set to a value of 3 and the currentvalue of the delay doubler, DELAY DOUBLER, which is initially set to avalue of 0).

The process then moves to step S10 in which the threshold valuesassociated with the stability level looked up in step S5 are obtainedfor use in the remainder of the process and then the process proceeds tostep S15.

At step S15 the DLM function obtains the current error and re-synch datawhich it has received in respect of the present line being analysed.This is read from the daily data file which is sent to the DLM functionon a daily basis as described above. The process then proceeds to stepS20.

Step S20 is the step responsible for actually categorising lines intoone of four possible different categories: very poor, poor, OK and good.To do this both of the metrics used in the present embodiment, namelyno. of errors detected (at both the user modem and the network modem inthe DSLAM) and the number of re-synchs (as recorded by the DSLAM) arecompared (after normalisation as mentioned above) with variouscorresponding thresholds whose values are set according to the stabilitylevel to which the line is assigned. Table 2 below sets out the variousthresholds used in the present embodiment.

TABLE 2 Stability Metric Very Poor Poor OK Good Aggressive Re-Trains >10per hour Mtb < 3600 mtb < 8640 mtb ≧ 8640 Aggressive Errors — Mtb < 10mtb < 8640 mtb ≧ 8640 Normal Re-Trains >10 per hour Mtb < 7200 mtb <8640 mtb ≧ 8640 Normal Errors — Mtb < 300 mtb < 8640 mtb ≧ 8640 StableRe-Trains >10 per hour Mtb < 28800 mtb < 86400 mtb ≧ 86400 Stable Errors— Mtb < 1000 mtb < 28800 mtb ≧ 28800

In table 2 “mtb” stands for “mean time between” and thus corresponds tothe normalised metrics calculated by dividing the total time in secondsfor which the respective line has been in synchronisation over the past24 hour period of the monitoring by the number of re-trains or errorsrecorded in that period. For all cases, in the present embodiment, ifthere are more than 10 re-trains in any one hour period, the line isassumed to be very poor, regardless of the number of errors recorded.For lines operating at an aggressive stability level, if the mean timebetween retrains is less than 3600 seconds (=1 hour) (i.e. if there ison average more than one re-train per hour of up-time e.g. 6 re-trainsin less than 5 hours of “up-time”) (but the mtb retrains should begreater than 360 seconds—corresponding to the 10 re-trains per hourthreshold for determining the line to be very poor) or if the averagetime between errors is less than 10 seconds (of up-time), then the lineis deemed to be poor; if the average time between re-trains is less than2.4 hours (but more than one hour) or the average time between errors isless than once every 2.4 hours (but more than once every 10 seconds)then the line is deemed to be ok, whereas if the average time betweenre-trains is greater than or equal to 2.4 hours and the average timebetween errors is greater than or equal to 2.4 hours, then the line isdeemed to be good. From Table 2 above, it is clear what the thresholdsare for the other stability levels in the same way.

In an alternative embodiment, the stability levels could operate suchthat for the most aggressive stability level the DLM function attemptsto keep sync loses to below 12 per 24 hour period (including switchingoff modems/routers which count as a sync loss) and to keep the lineerror free for 98.3% (59/60 seconds) of uptime measured over a 24 hourperiod; for the normal stability level the DLM function attempts to keepsync loses to below 6 per 24 hour period and to keep the line error freefor 99.8% (599/600 seconds) of uptime measured over a 24 hour period;and for the stable stability level the DLM function attempts to keepsync loses to below 3 per 24 hour period and to keep the line error freemore than 99.98% (5999/6000 seconds) of uptime measured over a 24 hourperiod.

Having categorised the line according to Table 2 (or some similarmechanism) in step S20 the process proceeds to step S25 where it isdetermined if the line has been categorised as being “poor/very poor,OK, or good”. If the line is categorised as being poor/very poor, theprocess proceeds to step S30 in which it is determined if the line hasbeen categorised as very poor or poor. If at step S30 it is determinedthat the line has been categorised as very poor then the processproceeds to step S35 in which an OSS request is issued for the line DLMprofile to be transitioned 2 steps in the less aggressive direction,provided it is at least two steps above the minimally aggressive level(which, in the present embodiment is 15 dB, Interleaved as is clear formTable 1), otherwise it just transitions straight to this minimallyaggressive level; if the line is already at this minimally aggressivelevel, it remains there but a fault is flagged to the system forattention by an engineer. Upon completion of step S35, the methodproceeds to step S60.

If at step S30 it is determined that the line has been categorised aspoor, the process proceeds to step S40 in which it is determined if thepoor delay counter is less than the poor threshold. If so, the methodproceeds to step S45 in which the poor delay counter is incremented (byone) and then the method proceeds to step S50 in which the good delaycounter is decremented (by one). Upon completion of step S50, theprocess ends (for the respective line). If at step S40 it is determined,on the other hand, that the delay counter equals (or exceeds) the poorthreshold, then the method proceeds to step S55 in which an OSS requestis issued for the line DLM profile to be transitioned 1 step in the lessaggressive direction, provided it is not already at the minimallyaggressive level (which, in the present embodiment is 15 dB,Interleaved, as is clear form Table 1), otherwise it remains there (i.e.at the minimally aggressive level) but a fault is flagged to the systemfor attention by an engineer. Upon completion of step S55, the methodproceeds to step S60.

At step S60, which is arrived at either after performing a two step lessaggressive reprofiling in step S35 or after performing a one stepreprofiling in step S55, the delay doubler is incremented by one(provided it has not already reached its maximum value of 5 in whichcase it just stays at 5) and then the good threshold is reset accordingto the formula GOOD THRESHOLD=DEFAULT GOOD THRESHOLD*2EXP(DELAYDOUBLER). Finally in step S60, the poor and good delay counters are bothreset to zero. Upon completion of step S60, the method ends (for therespective line being processed) and the DLM function moves on toanalysing any further lines requiring analysis in the current 24 hourperiod batch process.

If at step S25 it is determined that the line is categorised as OK, thenthe process proceeds to step S65 in which the good and bad delaycounters are both decremented by one (although if a counter is alreadyat zero it is not decremented further but rather stays at zero). Thisdecrementing of the delay counters for lines which are categorised as OKensures that lines which are only occasionally good or only occasionallybad but mostly are OK, will remain on there current profile setting.Upon completion of step S65, the process (for the respective line beingprocessed) ends.

If at step S25 it is determined that the line is “good”, the methodproceeds to step S70 in which it is determined if the good delay counteris less than the good threshold. If so, the process proceeds to step S75in which the good delay counter for the line in question, (GOOD DELAY),is incremented (by one). Upon completion of step S75, the processproceeds to step S80 in which the poor delay counter (POOR DELAY) isdecremented; this helps to prevent lines which are typically good asoften as they are poor from being moved to a different profile. Uponcompletion of step S80, the process (for the respective line beingprocessed) ends.

If at step S70 it is determined that the good delay counter (GOOD DELAY)is not less than the good threshold (GOOD THRESHOLD)—i.e. it has reachedor exceeded the threshold—then the process proceeds to step S85 in whichan OSS request is made to transition the DLM profile of the line onestep in the more aggressive direction (provided it is not already at themost aggressive profile, which, in the present embodiment is 3 dBnon-interleaved mode, as is clear from Table 1, in which case it simplystays at this most aggressive profile). Upon completion of step S85, themethod proceeds to step S90 in which the delay counters, GOOD DELAY andPOOR DELAY, for the line is reset and then the process (for therespective line) ends. As mentioned above, once the process ends for thecurrent line being processed, the DLM function moves on to analysing anyfurther lines requiring analysis in the current 24 hour period batchprocess.

Variations

As a slight variant on the above described process, an AGGRESSIVEPROFILE flag can be used to track when a reprofiling has been made inthe more aggressive direction, and the delay doubler may be incrementedonly if a reprofiling has occurred in the less aggressive direction(immediately) after a reprofiling has been made in the more aggressivedirection. This helps to increase the delay before which a moreaggressive transition can be made only if there is evidence ofoscillation between different profiles. This functionality may beimplemented by including an additional step after (i.e. upon completionof) step S90 to set the AGGRESSIVE PROFILE flag to true (from a defaultsetting of false); and by amending step S60 such that the delay doubleris only incremented if the AGGRESSIVE PROFILE flag is set to true, andthen resetting the AGGRESSIVE PROFILE flag back to false afterincrementing the delay doubler.

In alternative embodiments, different methods could be used todistinguish user-caused re-trains and forced re-trains. For example,some special software could be installed on the user modem end (i.e.either to run on the user's p.c. connected to the end-user DSL modem, orto run on the DSL modem itself) to detect whenever the modem isseemingly disconnected by the user (e.g. by detecting that power to themodem has been lost—e.g. because the user has switched off the modem ordisconnected the power cable, etc; or by detecting that a telephonecable has been unplugged, etc.). Moreover, the various ADSL standardseven specify as an optional requirement that the ATU's (i.e. the ADSLmodems) should monitor for a loss of power and report this if requested.Unfortunately, this feature has not been widely implemented yet bymanufacturers of ADSL modems. For this reason, the approach described inthe preferred embodiment above of looking for transitions betweensperiods in which no connection is detected as being present and periodsin which a connection is detected as being present is preferred becauseit can be done with common existing modems without any modifications tothe modems or the users' pc's (or the software running thereon).

The invention claimed is:
 1. A method of operating an access networkincluding a plurality of data connections between end user devices andan aggregation transceiver device where the connections are aggregatedfor onward connection through the access network, the method comprising:storing a plurality of Dynamic Line Management, DLM, profiles, each ofwhich specifies a set of values for a plurality of parameters associatedwith the data connections; storing a plurality of stability policieseach of which specifies a stability level which in turn specifies, adesired level of stability for a data connection and a number of errorsor resynchronisations per unit of time detected on a data connectionwhich causes the data connection to be transitioned from one DLM profileto another; associating a stability policy with each data connection;for each data connection, monitoring the connection for the occurrenceof errors or resynchronisations; selecting one of said stored DLMprofiles to be applied to the connection in dependence on both theresults of monitoring the connection and the stability level associatedwith the data connection; and applying the selected profile to the dataconnection; wherein selecting one of said stored DLM profiles to beapplied to the connection includes transitioning to a different DLMprofile in the event that the number of detected errors orre-synchronisations per unit of time crosses a threshold and wherein thestability policies control the circumstances under which a connection istransitioned between different profiles such that different thresholdsapply to different stability policies.
 2. The method according to claim1 wherein the results of monitoring the stability of the connectioncomprise a value for each of one or more monitoring result parametersand wherein the selecting one of said stored DLM profiles comprisescomparing the value of the or each monitoring result parameter with acorresponding threshold and transitioning the data connection onto a newone of the stored profiles in the event that the comparison indicatesthat the threshold has been exceeded, wherein different correspondingthresholds are associated with different stability levels.
 3. The methodaccording to claim 2 wherein the monitoring result parameter, or one ofthe monitoring result parameters, is or depends upon the number offorced resynchronisations occurring on the data connection within apredetermined period of time.
 4. The method according to claim 1 whereinthe data connections are digital subscriber lines including remote andcentral transceiver units connected over a copper pair and operating inaccordance with one or more of the various xDSL standards agreed by theInternational Telecommunication Union.
 5. The method according to claim4 wherein the aggregation transceiver device is a Digital SubscriberLine Access Multiplexer comprising a plurality of central transceiverunits operating in accordance with an xDSL standard.
 6. The methodaccording to claim 1 wherein the DLM profile associated with a givendata connection and the stability level associated with that connectionare both stored within a device controlled by the operator of the accessnetwork.
 7. The method according to claim 1 wherein the stability levelassociated with a given data connection is stored within an end userdevice and wherein messages to the aggregation transceiver device aresent whose value depends upon the stored stability level.
 8. Amanagement device for use in an access network including a plurality ofdata connections between end user devices and an aggregation transceiverdevice where the connections are aggregated for onward connectionthrough the access network, the access network storing in associationwith each data connection a Dynamic Line Management, DLM, profile whichspecifies a set of values for a plurality of parameters associated withthe respective data connection, together with a stability levelspecifying a desired level of stability for the data connection, themanagement device comprising a processing system, including a computerprocessor, the processing system being configured to: receive monitoringdata specifying the number of errors or resynchronisations detected oneach data connection over a predetermined period of time; determinewhether each data connection should be transitioned onto a new profilein dependence upon both the monitoring data and the stability levelassociated with the data connection; select a new DLM profile to beapplied to each connection in the event that it is determined that thecorresponding data connection should be transitioned onto a new DLMprofile; and request an OSS system of the access network to apply theselected profile to the data connection; wherein the stability level isone of a plurality of different stability levels each of which may beapplied to a data connection, and wherein selecting a new DLM profile tobe applied to a data connection includes transitioning to a differentDLM profile in the event that the number of errors or resynchronisationsdetected on the data connection over a predetermined period of timecrosses a threshold and wherein the stability levels control thecircumstances under which a connection is transitioned between differentprofiles such that different thresholds apply to different stabilitylevels.
 9. An access network including a management device according toclaim
 8. 10. An end user device for use with an access network includingan aggregation transceiver device where a data connection from the enduser device is aggregated with other similar data connections from othersimilar end user devices for onward connection through the accessnetwork, the access network storing in association with each dataconnection a Dynamic Line Management, DLM, profile which specifies a setof values for a plurality of parameters associated with the respectivedata connection, the end user device comprising a processing system,including a computer processor, the processing system being configuredto: store a stability level specifying a desired level of stability ofthe data connection; and cause messages specifying monitoring dataindicative of the stability of the data connection over a predeterminedperiod of time to be sent to the aggregation device wherein the messagesare dependent on the stored level of stability.
 11. A non-transitorydata storage medium carrying a computer program or suite of computerprograms for causing the method of claim 1 to be carried out duringexecution of the program or programs.
 12. A management device for use inan access network including a plurality of data connections between enduser devices and an aggregation transceiver device where the connectionsare aggregated for onward connection through the access network, theaccess network storing in association with each data connection aDynamic Line Management, DLM, profile which specifies a set of valuesfor a plurality of parameters associated with the respective dataconnection, together with a stability level specifying a desired levelof stability for the data connection, the management device comprising:a receiver for receiving monitoring data specifying the number of errorsor resynchronisations detected on each data connection over apredetermined period of time; a processor operating in accordance with acomputer program code module for causing the processor to determinewhether each data connection should be transitioned onto a new profilein dependence upon both the monitoring data and the stability levelassociated with the data connection; the processor further operating inaccordance with a computer program code module for causing the processorto select a new DLM profile to be applied to each connection in theevent that the processor determines that the corresponding dataconnection should be transitioned onto a new DLM profile; and arequestor for requesting an OSS system of the access network to applythe selected profile to the data connection; wherein the stability levelis one of a plurality of different stability levels each of which may beapplied to a data connection, and wherein determining that thecorresponding data connection should be transitioned onto a new DLMprofile includes determining if the number of errors orresynchronisations detected on the data connection over a predeterminedperiod of time crosses a threshold and wherein the different stabilitylevels specify different values for the threshold such that differentthreshold values apply to different stability levels.